A Class of Sodium Transition‐Metal Sulfide Cathodes With Anion Redox
Jiarui He, Amruth Bhargav, John Okasinski, Arumugam Manthiram
Abstract
Abstract Sodium‐ion batteries (SIBs) are entering commercial relevance as a sustainable and low‐cost alternative to lithium‐ion batteries. Improving the energy density of SIBs is critical to enable their widespread adoption. Here, a new class of cathode materials Na 6 M S 4 ( M = Co, Mn, Fe, and Zn) that exhibit high charge‐storage capacity is reported. Using Na 6 CoS 4 as a prototypical example, a six‐electron conversion reaction dominated by anion redox is observed, confirmed through various electrochemical and spectroscopic techniques. After the initial cycle, Na 6 CoS 4 delivers a high capacity of 392 mA h g −1 with a long lifespan of over 500 cycles. The reaction involves, initially, the transformation of crystalline Na 6 CoS 4 to a nearly amorphous structure consisting of mainly CoS and sulfur nanoparticles, which then reversibly cycles between nearly amorphous a‐CoS/S and a‐Na 6 CoS 4 . Such anion‐redox‐driven conversion‐type cathodes hold the potential to enable energy‐dense, stable SIBs.